The driver does not monitor speed with the use of the speed camera or radar device. They use the speedometer to monitor vehicle speed against the speed limit.

So the question arises, does the legislation state anything with regard to the limits of error of vehicle speedometers.

Car Speedo

Under 202 of the Victorian Road Safety (Vehicles) Regulations 1999. We find a vehicle is eligible to be registered if it complies with the standards for registration.

Vic Regulations

The Victorian Road Safety (Vehicles) Regulations 1999, SCHEDULE 8—VEHICLE STANDARDS on page 239 states ;

“sets out standards that vehicles must comply with to be eligible for unconditional registration and to be driven on roads and road related areas.

This Schedule contains the Vehicle Standards that form the standards for registration under the Road Safety Act 1986.

The standards are intended… to promote…their (vehicle) safe use ”

Under PART 2—APPLICATION OF THE VEHICLE STANDARDS on page 244 states it states;

“The Vehicle Standards apply to motor vehicles and trailers on roads and road-related areas.”

Clause 20 on page 249 states;

If a third edition ADR applies to the design and construction of a vehicle, the vehicle must comply with the ADR.

Clause 18 states;

A "third edition ADR" is a national standard incorporated in the document described as the Australian Design Rules for Motor Vehicles and Trailers, Third Edition, published by the Federal Office of Road Safety of the Commonwealth Department of Transport and Regional Development.”

ADR's

Applicable to all vehicles registered prior to 1st July 2006.

PART C - CURRENT-ISSUE ADRs states;

"The ADRs in this Part have the force of law as national standards determined under section 7 of the Motor Vehicle Standards Act 1989."

ADR 18/02 under 18.5.1.1.2 states;

every vehicle must be fitted with a speedometer which must:

“indicate the actual vehicle speed, for all speeds above 40 km/h, to an accuracy of ± 10 per cent.”

This is the full text of the Standard:

18.5 SPEEDOMETERS AND ODOMETERS (ALL VEHICLES)
18.5.1 Speedometers
18.5.1.1 Unless otherwise ‘Approved’, every vehicle must be fitted with a speedometer which must:
18.5.1.1.1 indicate vehicle speed only in kilometres per hour; and
18.5.1.1.2 indicate the actual vehicle speed, for all speeds above 40 km/h, to an accuracy of ±10 per cent.
18.5.1.2 The speedometer must be installed so that its indication is readily visible to the driver when seated in the normal driving position.

Conclusion

The conclusion is that for the purposes of the regulations, a vehicle registered prior to July 1st 2006 traveling within ±10 per cent of the nominated speed limit should be considered to be traveling at the speed limit. i.e. a vehicle travelling between 54 and 66km/h should be considered under the Regulations to be traveling at 60km/h

Just as the legislation stipulates a limit of error on the speed measurement device, it also stipulates a limit of error on the vehicle speedometer.

The errors on both of these instruments needs to be taken into consideration when establishing a breach of the regulations.

Using a 60km/h speed zone as an example. A measured speed is reduced from 69 to 66 km/h to factor in the error of the speed camera and then a further 10% must be deducted for the vehicle speedometer. 10% of 66 km/h is 6 km/h = 60km/h. The speed limit on that road.